1. Field of the Invention
The present invention relates to a transmission rate control method, a mobile station, and a radio network controller.
2. Description of the Related Art
In a field of “Enhanced Uplink (EUL)”, a transmission rate control method, which can perform both of a common transmission rate control and a dedicated transmission rate control by using two “Absolute Grant (AG)”, is proposed.
One of the AG is a “Common Absolute Grant transmission rate control signal (Common Absolute Grant)” which is received at every mobile stations UE having the same ID (a common ID) located in the cell.
Other AG is a “Dedicated Absolute Grant transmission rate control signal (Dedicated Absolute Grant)” which is received at each mobile station having different ID respectively (See, Non-Patent Literature 1: 3GPP TSG-RAN R2-050929).
The AG is transmitted from a radio base station Node B to the mobile station UE through an “E-DCH AG Channel (E-AGCH)”. Each of the Common AG and the Dedicated AG can be paired with the different E-AGCH respectively, or can be paired with the same E-AGCH.
On the other hand, as shown in Non-Patent Literature 2 (3GPP TSG-RAN TS25.309 v6.2.0), a Transmission Time Interval (herein after, TTI) of an “Enhanced Dedicated Channel (E-DCH)” can be selected from “2 ms” and “10 ms”.
When the TTI is set to “2 ms”, it is possible to perform a detailed scheduled transmission. When the TTI is set to “10 ms”, it is possible to decrease an impact to downlink capacity by decreasing a downlink transmission power.
In other words, when the TTI of the E-DCH is set to “2 ms”, a frame length of layer-1 channel (E-AGCH/E-RGCH/E-HICH) in downlink which relates to the EUL becomes “2 ms”.
When the TTI of the E-DCH is set to “10 ms”, a frame length of the E-AGCH which relates to the EUL becomes “10 ms”, and a frame length of the E-RGCH and the E-HICH which relate to the EUL becomes “8 ms”.
Therefore, when the TTI of the E-DCH is set to “10 ms”, the frequency of transmitting the layer-1 channel in downlink which relates to the EUL is decreased, and it is possible to decrease the impact to downlink capacity.
As shown in Non-Patent Literature 2, the transmission rate control uses a method of designating, at a radio base station Node B, a transmission power offset (transmission power of Enhanced Dedicated Physical Data Channel/transmission power of Dedicated Physical Control Channel, i.e., a transmission power offset of the E-DPDCH to the DPCCH) to the mobile station using the AG, and determining, at the mobile station UE, a Transport Block Size (TBS) for transmitting uplink user data, based on a correspondence table associating the transmission power offset indicated by the received AG with the TBS.
However, when the E-DCH which has different TTI is controlled using the Common AG, the following problem can be occurred.
Here, an example of case that the TTI of the E-DCH are set to “2 ms” or “10 ms”, the minimum TBS is set to 200 bits, and the transmission power offset which corresponds to 60 kbps is notified as a scheduling signal through the Common AG, will be studied.
In this situation, when the TTI of the E-DCH is set to “10 ms”, the mobile station UE can transmit 600 bit (=60 kbps×10 ms) of uplink user data at each TTI (each HARQ process).
However, when the TTI of the E-DCH is set to “2 ms”, an amount of user data which can be transmitted at each TTI (each HARQ process) is 120 bit (60 kbps×2 ms), and does not reach to the minimum TBS (200 bit). Accordingly, when the TTI of the E-DCH is set to “2 ms”, the mobile station UE cannot transmit uplink user data at each TTI (each HARQ process).
In this situation, a method for transmitting the uplink user data by limiting HARQ processes to be used is conceivable.
For example, a method for transmitting the uplink user data, by limiting the HARQ process to be used to one HARQ process, and increasing a transmission power offset by “N” times (“N” indicated the maximum number of HARQ processes) is conceivable.
To be more specific, a method for transmitting, at the mobile station, the uplink user data with the transmission power offset increased by “N” times, at an HARQ process corresponding to a timing in which the Common AG has been received is conceivable.
However, in this situation, all of the mobile stations UE receive the Common AG at almost the same timing. Therefore, there is a problem that an interference power will be increased during a TTI of HRAQ process corresponding to the timing.